Various embodiments disclosed herein are directed to structure for attachment to body anatomy, and more particularly, towards approaches for providing mounting members for trans-articular implantable mechanical energy absorbing systems.
Joint replacement is one of the most common and successful operations in modern orthopaedic surgery. It consists of replacing painful, arthritic, worn or diseased parts of a joint with artificial surfaces shaped in such a way as to allow joint movement. Osteoarthritis is a common diagnosis leading to joint replacement. Such joint replacement procedures are a last resort treatment as they are highly invasive and require substantial periods of recovery. Total joint replacement, also known as total joint arthroplasty, is a procedure in which all articular surfaces at a joint are replaced. This contrasts with hemiarthroplasty (half arthroplasty) in which only one bone's articular surface at a joint is replaced and unincompartmental arthroplasty in which the articular surfaces of only one of multiple compartments at a joint (such as the surfaces of the thigh and shin bones on just the inner side or just the outer side at the knee) are replaced.
Arthroplasty, as a general term, is an orthopaedic procedure which surgically alters the natural joint in some way. Arthroplasty includes procedures in which the arthritic or dysfunctional joint surface is replaced with something else as well as procedures which are undertaken to reshape or realigning the joint by osteotomy or some other procedure. A previously popular form of arthroplasty was interpositional arthroplasty in which the joint was surgically altered by insertion of some other tissue like skin, muscle or tendon within the articular space to keep inflammatory surfaces apart. Another less popular arthroplasty is excisional arthroplasty in which articular surfaces are removed leaving scar tissue to fill in the gap. Among other types of arthroplasty are resection(al) arthroplasty, resurfacing arthroplasty, mold arthroplasty, cup arthroplasty, silicone replacement arthroplasty, and osteotomy to affect joint alignment or restore or modify joint congruity.
The most common arthroplasty procedures including joint replacement, osteotomy procedures and other procedures in which the joint surfaces are modified are highly invasive procedures and are characterized by relatively long recovery times. When it is successful, arthroplasty results in new joint surfaces which serve the same function in the joint as did the surfaces that were removed. Any chodrocytes (cells that control the creation and maintenance of articular joint surfaces), however, are either removed as part of the arthroplasty, or left to contend with the resulting new joint anatomy and injury. Because of this, none of these currently available therapies are chondro-protective.
A widely-applied type of osteotomy is one in which bones beside the joint are surgically cut and realigned to improve alignment in the joint. A misalignment due to injury or disease in a joint related to the direction of load can result in an imbalance of forces and pain in the affected joint. The goal of osteotomy is to surgically re-align the bones at a joint such as by cutting and reattaching part of one of the bones to change the joint alignment. This re-alignment relieves pain by equalizing forces across the joint. This can also increase the lifespan of the joint. The surgical realignment of the knee joint by high tibial osteotomy (HTO) (the surgical re-alignment of the upper end of the shin bone (tibia) to address knee malalignment) is an osteotomy procedure done to address osteoarthritis in the knee. When successful, HTO results in a decrease in pain and improved function. However, HTO does not address ligamentous instability—only mechanical alignment. Good early results associated with HTO often deteriorate over time.
Other approaches to treating osteoarthritis involve an analysis of loads which exist at a joint and attempts to correct (generally reduce) these loads. Both cartilage and bone are living tissues that respond and adapt to the loads they experience. Within a nominal range of loading, bone and cartilage remain healthy and viable. If the load falls below the nominal range for extended periods of time, bone and cartilage can become softer and weaker (atrophy). If the load rises above the nominal level for extended periods of time, bone can become stiffer and stronger (hypertrophy). Osteoarthritis or breakdown of cartilage due to wear and tear can also result from overloading. When cartilage breaks down, the bones rub together and cause further damage and pain. Finally, if the load rises too high, then abrupt failure of bone, cartilage and other tissues can result.
The treatment of osteoarthritis and other bone and cartilage conditions is severely hampered when a surgeon is not able to control and prescribe the levels of joint load. Furthermore, bone healing research has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of load over time, e.g. during a particular treatment schedule. Thus, there is a need for devices which facilitate the control of load on a joint undergoing treatment or therapy, to thereby enable use of the joint within a healthy loading zone.
Certain other approaches to treating osteoarthritis contemplate external devices such as braces or fixators which attempt to control the motion of the bones at a joint or apply cross-loads at a joint to shift load from one side of the joint to the other. A number of these approaches have had some success in alleviating pain. However, lack of patient compliance and the inability of the devices to facilitate and support the natural motion and function of the diseased joint have been problems with these external braces.
Prior approaches to treating osteoarthritis have also failed to account for all of the basic functions of the various structures of a joint in combination with its unique movement. In addition to addressing the loads and motions at a joint, an ultimately successful approach must also acknowledge the dampening and energy absorption functions of the anatomy. Prior devices designed to reduce the load transferred by the natural joint typically incorporate relatively rigid constructs that are incompressible. Mechanical energy (E) is the action of a force (F) through a distance (s) (i.e., E=F×s). Device constructs which are relatively rigid do not allow substantial energy storage as they do not allow substantial deformations - do not act through substantial distances. For these relatively rigid constructs, energy is transferred rather than stored or absorbed relative to a joint. By contrast, the natural joint is a construct comprised of elements of different compliance characteristics such as bone, cartilage, synovial fluid, muscles, tendons, ligaments, and other tissues. These dynamic elements include relatively compliant ones (ligaments, tendons, fluid, cartilage) which allow for substantial energy absorption and storage, and relatively stiffer ones (bone) that allow for efficient energy transfer. The cartilage in a joint compresses under applied force and the resultant force displacement product represents the energy absorbed by cartilage. The fluid content of cartilage also acts to stiffen its response to load applied quickly and dampen its response to loads applied slowly. In this way, cartilage acts to absorb and store, as well as to dissipate energy.
With the foregoing applications in mind, it has been found to be necessary to develop effective structures for mounting to body anatomy which conform to body anatomy and cooperate with body anatomy to achieve desired load reduction, energy absorption, energy storage, and energy transfer. The structure should also provide a base for attachment of complementary structure across articulating joints.
For these implant structures to function optimally, they should not cause a disturbance to apposing tissue in the body, nor should their function be affected by anatomical tissue. Moreover, there is a need to reliably and durably transfer loads across members defining a joint. Such transfer can only be accomplished where the base structure is securely affixed to anatomy. It has also been found desirable that a base have a smaller bone contact footprint. In this way, a less invasive implantable procedure can be possible, surgical time can be decreased, and larger variations in and greater members of patients can be accommodated with the same base geometries.
Therefore, what is needed is an effective base for connecting an implantable trans-articular assembly and one which does so with a reduced or minimized bone contacting surface area.